1. Field of the Invention
The present invention relates to a fluid-pressure apparatus for controlling a slave member to follow a master member in motion.
2. Description of the Prior Art
Conventional master/slave actuator apparatuses include an electro-hydraulic servo valve which are supplied with an electrical signal responsive to angular displacement of a master arm and another electrical signal responsive to angular displacement of a slave arm for controlling a hydraulic actuator which drives the slave arm so as to follow the master arm in angular motion.
As is well known, the electro-hydraulic servo valve is of poor reliability and tends to malfunction when used in adverse environments. More specifically, dirt in hydraulic operating fluid is likely to get jammed in the orifice of a nozzle-flapper or the small clearance around a spool. The magnetic characteristics of a solenoid coil may be changed due to drastic changes in ambient temperature, resulting in malfunctioning of the value. The valve is liable to operate improperly when the hydraulic operating oil is heated with resulting changes in viscosity and expansion of a spool. The electro-hydraulic servo valve is also disadvantageous in that its manufacture requires high precision and hence is expensive to manufacture. The master/slave actuator apparatuses which rely on such an electro-hydraulic servo valve are accordingly not reliable in operation in harmful applications and are costly to construct. Such apparatuses have found little use in rugged applications such as for example manipulators in foundries and smith shops, tunnel boring machines, construction machines, loading and unloading machines, or machines for use in ocean development.